1. Field of the Invention
The present invention relates to a disk device, such as a floppy disk drive device, for use as an external data storage device in a computer system.
2. Description of the Prior Art
A conventional disk device will be described below, taking a floppy disk drive device (hereinafter called an FDD device) as an example. An FDD device performs read/write operations to read and write data through a magnetic head from and to a floppy disk (hereinafter called an FD), which has a plurality of tracks arranged concentrically. An FD has 81 tracks, which are identified with numbers increasing from the outermost track, called track 1, to the innermost track, called track 81. The initial position (retract position) of the magnetic head is located further outside the outermost track of the FD, and is called track 0.
During a read/write operation on the FD, whereas the magnetic head is positioned at the target track by being driven stepwise in a radial direction with respect to the FD, the FD is rotated at a constant linear speed by a spindle motor. As a result, the magnetic head scans the FD along the track.
A typical means of driving the magnetic head stepwise in a radial direction with respect to the FD is the use of a stepping motor. The operation of such a stepping motor is controlled with a direction signal and step pulses (i.e. a pulse signal for stepping) supplied from a host (CPU). Specifically, the stepping motor drives the magnetic head in the direction specified by the direction signal by so many steps as the number of step pulses. The track at which the magnetic head is currently located is detected by the use of a track counter that counts step pulses.
In the conventional FDD device, no read/write operation on the FD is permitted until a predetermined period of time TA elapses after the spindle motor starts rotating. This predetermined period of time TA is the length of time required for the rotation rate of the spindle motor to stabilize at 300 to 360 rpm (revolutions per minute), and is typically set at about TA=500 milliseconds.
However, in the conventional FDD device, when step pulses are fed thereto from the host, the stepping motor is immediately driven in synchronism therewith. Thus, even while no read/write operation on the FD is permitted yet, the magnetic head is driven stepwise, with the result that the magnetic head is held at the target track for an unnecessarily long period of time. This leads to unnecessarily high consumption of electric power without any exchange of data.
Moreover, with the conventional FDD device, a mechanical shock or the like delivered thereto may cause the magnetic head to be displaced with no regard to step pulses. This leads to malfunctioning of the stepwise driving of the magnetic head and results in a seek error. In the event of a seek error, the host feeds step pulses to the FDD device to instruct it to retract the magnetic head to its initial position, i.e. track 0.
Here, if the mechanical shock or the like happens to have displaced the magnetic head outward relative to the position where it should be located, even if the magnetic head has already been retracted to track 0 by the step pulses, the output of the track counter erroneously indicates that the magnetic head has not yet been retracted to track 0. Once the FDD device gets into this state, it can no longer correctly perform the stepwise driving of the magnetic head. This state is cleared only by turning the power off once.
To avoid this inconvenience, the conventional FDD device is equipped with a reset circuit that resets the count of the track counter to 0 when the magnetic head is located at track 0 and in addition the direction signal points outward. This reset circuit makes the track at which the magnetic head is actually located coincide with the output of the track counter, and thereby prevents erroneous indication as mentioned above. After such resetting, the magnetic head is driven stepwise again according to step pulses fed thereto as a retrial instruction from the host, so that the magnetic head is moved back to the track at which it was located before the mechanical shock was delivered.
However, in the conventional FDD device, to permit the magnetic head that has been retracted to its initial position, i.e. track 0, to be moved back to the track at which it was located before a mechanical shock was delivered, it is inevitable to wait for step pulses to be fed thereto as a retrial instruction from the host, and thus recovery of the magnetic head position takes rather a long time. Moreover, on the part of the host, part of its processing power needs to be used for the recovery of the magnetic head position, and thus other operations are affected to no small extent.
An object of the present invention is to provide a disk device that saves electric power consumption by reducing the period of time for which the magnetic head is held at the target track without permission to access the disk.
Another object of the present invention is to provide a disk device that permits the magnetic head that has been retracted to its initial position because of an error in the stepwise driving thereof to be promptly moved back to the position where it was located before the error.
To achieve the above objects, according to one aspect of the present invention, in a disk device that drives a head stepwise relative to a disk, the head is inhibited from being driven stepwise until a predetermined period of time elapses after the disk starts being rotated.
According to another aspect of the present invention, in a disk device that drives a head stepwise relative to a disk, when the head is retracted to the initial position thereof on occurrence of an error in the stepwise driving thereof, the head is, by self recovery, moved back to the position where the head was located before the error without waiting for an instruction from outside.